The invention relates generally to metal cutting systems, and more particularly, to systems and methods for forming a first plasma arc between an electrode and a tip of a plasma cutter then transferring that arc such that it forms a second plasma arc between the electrode and the work lead.
A plasma cutting system harnesses the energy in plasma (e.g., high temperature ionized gas) to cut metal or other electrically conductive material. Prior to cutting, the first plasma arc, the pilot arc, is struck between the negatively charged electrode and the tip of the plasma cutter. The arc must then be transferred to the work piece to initiate cutting. The tip to work potential determines the favorability of the plasma shift from the tip to the workpiece and thus the transfer height (i.e., the height at which the pilot arc will transfer and become the cutting arc) of the system. Since a large transfer height is desirable, multiple methods, such as the placement of resistors in series with the pilot switch, are currently employed to increase the tip to work potential. However, these methods fail to maximize transfer height and often lead to lossy circuits.
After a pilot arc has been established, it is necessary to detect that current will readily flow to the work piece so that cutting current can be applied and the pilot circuit can be disabled. Since the arc transfer is a critical step in the initiation of plasma cutting, this requires a precise and accurate measurement technique. Traditionally, a work current sensor, such as a Hall-based current sensor, is connected to the work lead to measure the current in the work lead prior to transfer. However, it is now recognized that these sensors are costly and comprise a large portion of the overall machine cost. Accordingly, it is now recognized that there exists a need for plasma cutting systems equipped to maximize transfer heights and tip to work potential while minimizing cost.